Electrochemical evaluation of LiNi0.5Mn0.3Co0.2O2, LiNi0.6Mn0.2Co0.2O2, and LiNi0.8Mn0.1Co0.1O2 cathode materials for lithium-ion batteries: from half-coin cell to pouch cell

Three types of lithium nickel–manganese–cobalt oxide (NMC) cathode materials (NMC532, NMC622, and NMC811) proposed for use in lithium-ion batteries were evaluated and compared by electrochemical methods. It was found how each transition metal (Ni, Mn, and Co) in this ternary compound affects the electrochemical performance of the cathode materials. Based on cyclic voltammetry, all three materials require pre-cycling to attain a suitable structure for electrochemical reactions. Ni and Co controlled the initial capacity of the materials, but capacity retention during cycling was determined by the stability of the material, which is balanced by the ratio adjusting of Ni, Mn, and Co. Mn and Co provide chemical stability and structural stability for NMC materials, respectively. The voltage decay in the NMC811 was less than the others due to the presence of higher amounts of Ni2+ and Ni3+, which have a much smaller radius than lithium-ion and less cation mixing. The capacity retention of NMC622 at high rates was higher than the other two materials. The combination of galvanostatic intermittent titration technique (GITT), cyclic voltammetry at different scan rates, and intercalation isotherm showed that the diffusion coefficient of lithium ion for NMC622 is higher than the other two materials. Electrochemical impedance spectroscopy showed that the resistance of the surface layer is lower in NMC622 than the others in different lithium-ion concentrations. The self-discharge test showed the superiority of NMC811 over the others. Considering all performance factors, NMC622 and NMC811 are efficient materials for various applications, especially electric vehicles.Graphical abstract